Rear wheel steering device for motor bicycle

Description: TECHNICAL FIELD [Detailed description of the invention]

[Industrial application field] The present invention relates to a rear wheel steering device in which the rear wheels are also steered in response to a turning operation such as steering the front wheels of a motorcycle or shifting the weight of the driver, and in particular, a structure for connecting the rear wheel support member to the vehicle body. By devising the above, the rear wheels are naturally steered by the lateral force acting on the rear wheels without providing a special steering mechanism that forcibly steers the rear wheels according to the steering of the front wheels. Regarding the rear wheel steering device. [Conventional technology] In the past, it was common for motorcycles to steer only the front wheels, but recently, by steering the rear wheels as well as the front wheels, for example, improving running stability in the middle and high speed ranges, or in the low speed range. It is considered to reduce the turning radius of. As a front and rear wheel steering device for such a motorcycle, for example, a front fork to which a steering handle is attached and a rear wheel supported so as to be able to turn left and right are connected via a transmission link interposed with a cam mechanism. (See, for example, Japanese Patent Application Laid-Open No. 61-178275). [Problems to be solved by the invention] Since the above-mentioned conventional device has a structure in which the rear wheels are forcibly steered in conjunction with the operation of the steering wheel, there is a drawback that the structure becomes complicated because a conduction link, a cam mechanism, etc. are required. The present invention has been made in view of the above-mentioned conventional situation, and has a simple configuration in which the connection structure of the rear wheel support member with the vehicle body is simply devised, and the rear wheels are naturally steered by the lateral force acting on the rear wheels. It is an object of the present invention to provide a rear wheel steering device for a motorcycle that has been made possible. [Means to solve problems] In the present invention, the rear wheels are pivotally supported by the rear end portion of the rear wheel support member, and the front end portion of the rear wheel support member is attached to the vehicle body frame by a pair of left and right link members arranged across the vehicle axis. The link extension lines that are swingably connected up and down and connect the shaft fulcrums on the vehicle body side and the rear wheel support member side of the left and right link members intersect substantially on the vehicle axis when viewed from the plane. The link member is a rear wheel steering device for a motorcycle, which is capable of swinging up and down and swinging in a plane including the above four shaft fulcrums. Here, when the link extension lines connecting the front and rear shaft fulcrums of the left and right link members of the present invention intersect on the vehicle axis, both link members are arranged non-parallel to each other, and the lines connecting the four shaft fulcrums are trapezoidal. It means that you are doing. In this case, the intersection of the extension lines of both links is behind and in front of the point of action of the lateral force on the rear wheels (the grounding point of the rear wheels, which is within a range of several cm in front and behind the position directly below the axle). Both cases are included. Which position to set this intersection will be determined according to the steering characteristics to be obtained, as will be described later. Further, the point at which both link members can swing in a plane including four shaft fulcrums can be realized by interposing a rubber bush, a spherical joint, or the like in the shaft fulcrums. [Action] In the rear wheel steering device according to the present invention, since the left and right link members are arranged non-parallel, the moment for steering the left and right link members to the rear wheels by the lateral force acting on the rear wheels during turning (so-called cornering force, canvas last). Works. In the present invention, since the link member is configured to be swingable in a plane including four shaft fulcrums, the rear wheel support member swings due to the moment, and the rear wheels are naturally steered by this moment. Become. When the intersection of the extension lines of both links is set behind the point of action of the lateral force on the rear wheels, the rear wheels are steered in the same direction (in phase) as the front wheels, and therefore running stability in the middle and high speed ranges. Is improved. On the other hand, when the intersection is set ahead of the point of action, the rear wheels are steered in the opposite direction (opposite phase) to the front wheels, the radius of gyration is reduced, and it is advantageous when the vehicle makes a small turn at low speed. [Example] Hereinafter, examples of the present invention will be described with reference to the drawings. FIGS. 1 to 5 are diagrams for explaining a rear wheel steering device for a motorcycle according to an embodiment of the present invention. In the figure, reference numeral 1 denotes a scooter-type motorcycle in which the present embodiment is adopted, which is shown with the vehicle body cover and the like removed. The body frame 2 of the motorcycle 1 has a pair of left and right side pipes 4b connected to the rear end of the main pipe 4a which is connected to the head pipe 3 and extends downward, and the side pipes 4b are extended from above to rear. It is composed. The steering shaft 6a of the front fork 6 that pivotally supports the front wheel 5 at the lower end is pivotally supported by the head pipe 3, and the steering handle 7 is fixed to the rear end of the steering shaft 6a. The engine unit 8 is connected by a pair of left and right link members 15 and 16 near the rising portion of the left and right side pipes 4b. The engine unit 8 is mainly composed of an engine body 9 in which a cylinder and a cylinder head are laminated on a crankcase, and a transmission case 10 integrally formed with the crankcase, and is rearward at the rear end of the transmission case 10. A ring 11 is pivotally supported, and a shock absorber 12 is arranged between the rear end portion thereof and the rear portion of the left side pipe 4b. That is, the engine unit 8 is a rear shaft support member that pivotally supports the rear wheels 11. Note that 13 is an air cleaner and 14 is a vaporizer. The pair of left and right link members 15 and 16 have bushes 17 and 17 formed at the front end of the rod-shaped member and brackets 18 and 18 formed at the rear end, respectively, and the distance between the brackets 18 and 18 is the bush 17, It is narrower than the interval between 17 and has a trapezoidal shape as a whole. Further, the bush 17 is formed by inserting a rubber body 17c between the outer cylinder 17a and the inner cylinder 17b fixed to the rod-shaped member and baking and fixing the bush 17. Further, the rubber body 17c is formed with slits 17d in the axial direction, so that the rigidity of the central portion is high and the rigidity of both ends is low. As a result, the rubber body 17c is relatively easy to bend in the direction perpendicular to the axis, and hardly deforms in the front-rear direction. The bush 17 is supported by a support pin 19 on a support piece 4c fixed to the side pipe 4b. Further, the bracket 18 has a U-shape in a plan view, and is supported by a support pin 19 via a bush 20 formed on the front wall of the crankcase. The bush 20 has the same structure as the bush 17. As a result, both the link members 15 and 16 support the engine unit 8 so as to swing up and down with respect to the vehicle body, and can swing in a plane including the four bushes 17, 17, 20, 20. There is. Further, the link extension lines L connecting the shaft fulcrums of both bushes 17 and 20 are on the vehicle axis l projected on the road surface G and the rear wheels 11 as shown in FIG. 1 when viewed from a plane. As shown in FIG. 2, the two link extension lines L intersect with each other below the road surface G when viewed from the rear or front of the vehicle. Next, the action and effect of this example will be described. While the motorcycle 1 of this embodiment is running, when the front wheel 5 is rotated to the left and turned to the left as shown in FIG. 5, the ground contact point of the rear wheel 11 (a point substantially directly below the axle 10a) is reached. In, a lateral force F having a magnitude corresponding to the centrifugal force and toward the center of rotation acts. When this is viewed from a plane, as shown in Fig. (A), the intersection O between the link extension lines L of the left and right link members 15 and 16 is behind due to the action point of the lateral force F, so the rear wheels A counterclockwise moment centered on the intersection O acts on 11 and the engine unit 8 that supports it, so that both link members 15 and 16 are centered on the bush 20 side, which is the shaft fulcrum on the engine side. It moves to the side, and as a result, the rear wheel 11 rotates slightly like the front wheel 5. Looking at the action of this lateral force from the rear, as shown in Fig. (B), the intersection O is below the ground contact point (the point of action of the lateral force F), so the rear wheels 11 and eventually the engine unit 8 A counterclockwise moment centered on the intersection O acts on the above, so that the bush 20 side of both link members 15 and 16 moves inward in turning, and as a result, the rear wheel 11 inclines inward. As described above, in the present embodiment, the link members 15 and 16 are positioned so that the intersection O of these extension lines L is located behind the axle 10a when viewed from the plane and below the road surface G when viewed from the back. When viewed from the plane, it rotates in the same phase as the front wheel 5, and when viewed from the back, it inclines inward, which can improve the running stability during medium and high speed running. Here, in the above embodiment, rubber bushes are provided at the front and rear ends of both link members, but this does not necessarily have to be a rubber bush, and in short, it can swing in a plane including four shaft fulcrums. Any structure that can support it will do. For example, as shown in FIG. 6, those having spherical bearings 21 on either one or both of the engine side and the vehicle body side can be adopted. Further, in the above embodiment, the case where the intersection O between the link extension lines L is set behind the axle 10a and below the ground contact point has been described, but in the present invention, the intersection O is set ahead of the axle 10a. It can also be set above the grounding point. FIG. 7 shows an example in which the distance between the bushes 20 is further narrowed and the intersection O is set to the front side of the axle 10a in the above embodiment, and FIG. 8 shows an example in which the distance between the bushes 20 is widened on the contrary. This is an example in which the intersection O is set in front of the bush 17. In either case, the lateral force F generates a clockwise moment around the intersection O, and in the case of Fig. 7, the bush 20 side moves to the outside of the turn, and in the case of Fig. 8, the bush 20 side moves to the inside of the turn. As a result, the rear wheels 11 are steered in the opposite phase to the front wheels 5. FIG. 9 shows an example in which the intersection O seen from the back surface of the link extension lines L is set above the road surface G. In this case, the rear wheel 11 is tilted to the outside of the turn due to the lateral force F. In the example of FIGS. 7 to 9 above, since the rear wheels are steered in the opposite phase to the front wheels, the turning radius becomes small. In the above embodiment, a motorcycle equipped with a unit swivel engine in which the engine unit is also used as a rear wheel support member has been described. However, the present invention describes a case where the rear wheels are pivotally supported by a normal rear arm. Of course, it can also be applied to. [Effect of the invention] As described above, according to the rear wheel steering device of the motorcycle according to the present invention, the rear wheel support members are connected to the vehicle body by a pair of left and right link members, and the extension lines of the two link members are substantially on the vehicle axis. Since both link members can swing up and down and swing in a plane including the four shaft fulcrums, the rear wheels can be steered by the lateral force generated during turning. There is an effect that rear wheel steering can be realized without providing a complicated mechanism.

[Simple explanation of drawings]

1 to 5 are views for explaining a rear wheel steering device of a motorcycle according to an embodiment of the present invention, FIG. 1 is a plan view, FIG. 2 is a rear view, and FIG. 3 (a). ) Is a cross-sectional plan view of the link member portion, FIG. 3 (b) is a side view of the bush, FIG. 4 is a side view of a motorcycle to which the embodiment device is applied, and FIGS. Is a plan view and a rear view schematically shown for explaining the operation, FIG. 6 is a sectional plan view showing a modified example of the link member, and FIGS. 7 to 9 are other embodiments of the present invention, respectively. It is a top view, a plan view, and a rear view schematically shown. In the figure, 1 is a motorcycle, 4b is a side pipe (body frame), 8 is an engine unit (rear wheel support member), 11 is a rear wheel, 15 and 16 are a pair of left and right link members, and 17 and 20 are bushes. (Axis fulcrum), l is the vehicle axis, L is the link extension line, and O is the intersection.